Special issue: Workflow in grid systems

A number of significant general issues for workflow authoring and enactment in Grid systems are discussed. A number of significant workflow systems are also proposed, which address the 'cyclic graph model' with compositional tools based on a graphical layout system that allows users to move components. The workflow systems are interposed between users, data, and services without considering the trust responsibilities that this design imposes on planning and enactment systems. A Systems Design approach separates enactment and protection by refactoring the protection requirements away from planning and enactment into the distributed system is required in a workflow system. One of the many possible ways to distinguish workflow computations on Grids is to consider a simple complexity scale. It is shown how different people and groups within collaborative communities can cooperatively constrain workflows by introducing constraints in a contextual form.